In vitro medical diagnostic tests are widely used to detect abnormalities in body fluids as an aid in diagnosing disease. Much of this testing occurs in hospital laboratories or reference laboratories that process a large number of body fluid samples in complex, highly automated, expensive instruments that require routine costly maintenance and require highly skilled operators to perform and interpret the tests and insure that the instruments are operating properly.
Since laboratory systems are large and complex, they cannot be used by individuals at home, in most doctors' offices or even in outpatient clinics or emergency rooms. There is a need for testing in these settings to reduce the need of transporting samples to remote laboratories and providing more immediate answers that can alter patient behavior or physician interventions and treatment on a timely basis.
To meet the need for such point of care testing, several systems have already been developed. Most notable are the widespread use of glucose test meters for monitoring blood glucose levels as an aid in controlling insulin use and altering dietary habits of diabetics. Dry chemistry test strips without an instrument have been used for detecting abnormalities in urine (urinalysis), bleeding of the bowel using stool samples and pregnancy using urine test strips. Diagnostic manufacturers have developed some systems for detecting cells in blood and urine that are less complex than the central laboratory equivalents but these systems are still quite costly and complex to operate and so do not fulfill the need for a true point of care device for hematology. Point of care systems for immunoassays using instrumentation have been largely unsuccessful to date.
Notably, there is no single instrument or technology that can perform the broad range of tests typically performed in a hospital laboratory since laboratory analyzers use widely different technologies to achieve the demanding requirements of sensitivity and accuracy that these types of assays require. It would be highly desirable to have an instrument that can perform a broad range of tests since users would only need to purchase one instrument. This would not only reduce the initial investment but would also reduce the complexity of operating and maintaining many different devices.
Until recently design of a point of care microscope using digital imaging has been impractical. Digital imaging of microscopic samples has been done for some time in research laboratories. Until recently sensors used in these systems were expensive. Also, until recently sensors had a limited number of pixels making resolution of microscopic digital images of poor quality and only permitting a small field of view. This limitation often made it difficult to accurately identify and classify body fluid particles and at the same time view a large enough volume to provide accurate counting statistics. Also, until recently irradiation sources for sensors used in microscopy were both expensive, difficult to maintain and difficult to use in a simple design.
The past ten years has witnessed dramatic improvements in CMOS and CCD technology that has dramatically reduced the price and improved the resolution of imaging sensors. There has also been a revolution in electromagnetic irradiation sources (most notably LED technology) that makes it possible to irradiate microscopic samples for transmission, scattering, fluorescence and phosphorescence. These technological advances now permit the design of systems that employ these components in novel ways to achieve digital microscopy that is inexpensive, high quality and versatile. With the use of CMOS sensors that have response to irradiation and sensitivity comparable to detectors used in central laboratory systems, it is possible to use a digital microscope using CMOS sensors to perform chemistry and immunoassay tests with characteristics similar to hospital laboratory systems.
Existing hospital laboratory instruments also have deficiencies in spite of their cost and complexity. For example, in laboratory flow cytometers used for hematology and urinalysis, the assumption is that particles flowing past the detector are widely separated from interfering particles so that any signals derived comes from a single particle without background interference. This leads, for example, to errors in identification and classification of red and white blood cells when amorphic crystals are present in urine samples analyzed with Sysmex analyzers. All laboratory cytometers using flow analysis (flow cytometers) must use expensive laser light sources to achieve the irradiation intensities required to detect a signal from a single cell passing the source at high speed even when highly sensitive and expensive photomultiplier detectors are used. This approach requires irradiation, irradiation detection components and complex fluidic control that are both expensive and require operation and maintenance by highly trained personnel. The present invention overcomes all of these limitations in particle identification, classification and counting at a lower cost and with less complexity.
Immunoassays usually require complex instruments that coordinate multiple reaction steps to achieve the high sensitivity and specificity required by many immunoassays. Typically, immunoassays require a separation step. This step in particular requires complex mechanical and fluid handling operations that make a low cost analyzer impractical. The present invention eliminates the need for washing and so makes immunoassays using the detection approach described in this invention of reduced cost and complexity—characteristics desirable in a point of care device.